Quantification of myocardial blood flow with dynamic perfusion 3.0 Tesla MRI: Validation with (15) O-water PET.

BACKGROUND: To develop and validate a method for quantifying myocardial blood flow (MBF) using dynamic perfusion magnetic resonance imaging (MBFMRI ) at 3.0 Tesla (T) and compare the findings with those of (15) O-water positron emission tomography (MBFPET ). METHODS: Twenty healthy male volunteers underwent magnetic resonance imaging (MRI) and (15) O-water positron emission tomography (PET) at rest and during adenosine triphosphate infusion. The single-tissue compartment model was used to estimate the inflow rate constant (K1). We estimated the extraction fraction of Gd-DTPA using K1 and MBF values obtained from (15) O-water PET for the first 10 subjects. For validation, we calculated MBFMRI values for the remaining 10 subjects and compared them with the MBFPET values. In addition, we compared MBFMRI values of 10 patients with coronary artery disease with those of healthy subjects. RESULTS: The mean resting and stress MBFMRI values were 0.76 ± 0.10 and 3.04 ± 0.82 mL/min/g, respectively, and showed excellent correlation with the mean MBFPET values (r = 0.96, P < 0.01). The mean stress MBFMRI value was significantly lower for the patients (1.92 ± 0.37) than for the healthy subjects (P < 0.001). CONCLUSION: The use of dynamic perfusion MRI at 3T is useful for estimating MBF and can be applied for patients with coronary artery disease.

Mechanistic insights into the oxidation of substituted phenols via hydrogen atom abstraction by a cupric-superoxo complex.

To obtain mechanistic insights into the inherent reactivity patterns for copper(I)-O2 adducts, a new cupric-superoxo complex [(DMM-tmpa)Cu(II)(O2(•-))](+) (2) [DMM-tmpa = tris((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)amine] has been synthesized and studied in phenol oxidation-oxygenation reactions. Compound 2 is characterized by UV-vis, resonance Raman, and EPR spectroscopies. Its reactions with a series of para-substituted 2,6-di-tert-butylphenols (p-X-DTBPs) afford 2,6-di-tert-butyl-1,4-benzoquinone (DTBQ) in up to 50% yields. Significant deuterium kinetic isotope effects and a positive correlation of second-order rate constants (k2) compared to rate constants for p-X-DTBPs plus cumylperoxyl radical reactions indicate a mechanism that involves rate-limiting hydrogen atom transfer (HAT). A weak correlation of (k(B)T/e) ln k2 versus E(ox) of p-X-DTBP indicates that the HAT reactions proceed via a partial transfer of charge rather than a complete transfer of charge in the electron transfer/proton transfer pathway. Product analyses, (18)O-labeling experiments, and separate reactivity employing the 2,4,6-tri-tert-butylphenoxyl radical provide further mechanistic insights. After initial HAT, a second molar equiv of 2 couples to the phenoxyl radical initially formed, giving a Cu(II)-OO-(ArO') intermediate, which proceeds in the case of p-OR-DTBP substrates via a two-electron oxidation reaction involving hydrolysis steps which liberate H2O2 and the corresponding alcohol. By contrast, four-electron oxygenation (O-O cleavage) mainly occurs for p-R-DTBP which gives (18)O-labeled DTBQ and elimination of the R group.

Online oxygen kinetic isotope effects using membrane inlet mass spectrometry can differentiate between oxidases for mechanistic studies and calculation of their contributions to oxygen consumption in whole tissues.

The reduction chemistry of molecular oxygen underpins the energy metabolism of multicellular organisms, liberating free energy needed to catalyze a plethora of enzymatic reactions. Measuring the isotope signatures of (16)O and (18)O during O2 reduction can provide insights into both kinetic and equilibrium isotope effects. However, current methods to measure O2 isotope signatures are time-consuming and disruptive. This paper describes the application of membrane inlet mass spectrometry to determine the oxygen isotope discrimination of a range of O2-consuming reactions, providing a rapid and convenient method for determining these values. A survey of oxygenase and oxidase reactions provides new insights into previously uncharacterized amino acid oxidase enzymes. Liquid and gas phase measurements show the ease of assays using this approach for purified enzymes, biological extracts and intact tissues.

Quantification of regional myocardial blood flow estimation with three-dimensional dynamic rubidium-82 PET and modified spillover correction model.

PURPOSE: Myocardial blood flow (MBF) estimation with (82)Rubidium ((82)Rb) positron emission tomography (PET) is technically difficult because of the high spillover between regions of interest, especially due to the long positron range. We sought to develop a new algorithm to reduce the spillover in image-derived blood activity curves, using non-uniform weighted least-squares fitting. METHODS: Fourteen volunteers underwent imaging with both 3-dimensional (3D) (82)Rb and (15)O-water PET at rest and during pharmacological stress. Whole left ventricular (LV) (82)Rb MBF was estimated using a one-compartment model, including a myocardium-to-blood spillover correction to estimate the corresponding blood input function Ca(t)(whole). Regional K1 values were calculated using this uniform global input function, which simplifies equations and enables robust estimation of MBF. To assess the robustness of the modified algorithm, inter-operator repeatability of 3D (82)Rb MBF was compared with a previously established method. RESULTS: Whole LV correlation of (82)Rb MBF with (15)O-water MBF was better (P < .01) with the modified spillover correction method (r = 0.92 vs r = 0.60). The modified method also yielded significantly improved inter-operator repeatability of regional MBF quantification (r = 0.89) versus the established method (r = 0.82) (P < .01). CONCLUSION: A uniform global input function can suppress LV spillover into the image-derived blood input function, resulting in improved precision for MBF quantification with 3D (82)Rb PET.

Integrated PET/MRI scanner with oxygen-15 labeled gases for quantification of cerebral blood flow, cerebral blood volume, cerebral oxygen extraction fraction and cerebral metabolic rate of oxygen.

OBJECTIVES: Measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO2) by PET with oxygen-15 labeled gases is useful for diagnosis and treatment planning in cases of chronic occlusive cerebrovascular disease. In the present study, CBF, CBV, OEF and CMRO2 were measured using the integrated design of PET/MRI scanner system. This is a first attempt to measure cerebral perfusion and oxygen metabolism using PET/MRI with oxygen-15 labeled gases. METHODS: PET/MRI measurements with the steady-state method of oxygen-15 labeled gases, carbon monoxide (C15O), oxygen (15O2), and carbon dioxide (C15O2) were performed on nine healthy men. Two kinds of attenuation correction for PET were performed using MRI with Dixon sequence (DIXON) and Dixon sequence with model-based bone segmentation (DIXONbone). A real-time motion correction of PET images was also performed using simultaneously measured MR images to detect head motion. RESULTS: Mean and SD values of CBF, CBV, OEF, and CMRO2 in the cerebral cortices with attenuation correction by DIXON were 31 ± 4 mL/100 mL/min, 2.7 ± 0.2 mL/mL, 0.40 ± 0.07, and 2.5 ± 0.3 mL/100 mL/min without real-time motion correction, and 33 ± 4 mL/100 mL/min, 2.7 ± 0.2 mL/mL, 0.40 ± 0.07, and 2.6 ± 0.3 mL/100 mL/min with real-time motion correction, respectively. Values with of CBF, CBV, OEF, and CMRO2 with attenuation correction by DIXONbone were 35 ± 5 mL/100 mL/min, 2.8 ± 0.2 mL/mL, 0.40 ± 0.07, and 2.8 ± 0.3 mL/100 mL/min without real-time motion correction, and 38 ± 5 mL/100 mL/min, 2.8 ± 0.2 mL/mL, 0.40 ± 0.07, and 3.0 ± 0.4 mL/100 mL/min with real-time motion correction, respectively. CONCLUSIONS: Using PET/MRI with oxygen-15 labeled gases, CBF, CBV, OEF, and CMRO2 could be measured. Values of CBF, CBV, and CMRO2 measured with attenuation correction by DIXON were significantly lower than those measured with correction by DIXONbone. One of the reasons for this is that attenuation correction of DIXON does not take into consideration of the photon absorption by bone. OEF values, corresponding to ratios of CMRO2 to CBF, were not affected by attenuation correction methods. Values of CBF and CMRO2 with a real-time motion correction were significantly higher than those without correction. Using PET/MRI with adequate corrections, similar values of CBF, CBV, OEF, and CMRO2 as PET alone scanner system reported previously were obtained. TRAIL REGISTRATION: The UMIN clinical trial number: UMIN000033382.

Tumour perfusion assessment during regional hyperthermia treatment: comparison of temperature probe measurement with H(2)(15)O-PET perfusion.

PURPOSE: Hyperthermia treatment might increase tumour oxygenation and perfusion, as has been reported for experimental tumours. The present study was performed to investigate this hypothesis in patients undergoing regional hyperthermia treatment. METHODS: Thirteen patients with primary or recurrent pelvic tumours were included in this study. Prior to and up to one hour after regional hyperthermia, perfusion was quantitatively determined by H(2)(15)O-PET. The fused CT-PET images were used to extract tumour time-activity curves and to identify the catheter position. Perfusion was calculated from the total tumour time-activity curves and for the time-activity curves at the catheter site. Additionally, perfusion was calculated from the temperature-time curves measured using temperature probes. RESULTS: Perfusion values calculated using H(2)(15)O-PET and those deduced from temperature probe measurements are significantly correlated with a correlation coefficient, R = 0.21. The perfusion values deduced from the temperature measured in a body cavity do not provide information about average tumour perfusion. Perfusion values deduced from the temperature are overestimated for very poorly perfused tissues and underestimated for highly perfused tissues. CONCLUSIONS: Temperature measurement during hyperthermia may allow only determination of intermediate perfusion values.

Pharmaceutical preparation of oxygen-15 labelled molecular oxygen and carbon monoxide gasses in a hospital setting.

BACKGROUND: Clinical positron emission tomography (PET) requires safe and effective PET radiopharmaceuticals. Tracers used for measuring oxygen consumption and blood volume are [(15)O]O(2) and [(15)O]CO, respectively. In general, these oxygen-15 labelled tracers are produced using a cyclotron that accelerates deuterons onto a target filled with (14)N(2) containing a trace of oxygen. In recent years, cyclotrons have been developed that only are capable of accelerating protons. The purpose of this study was to validate and assess such a cyclotron for production and administration of oxygen-15 labelled gasses in an hospital setting. METHODS: An RDS111 cyclotron (Siemens-CTI, Knoxville, USA) was validated for bolus production of [(15)O]O(2) and [(15)O]CO gasses. In addition, equipment was developed to administer these tracers to patients. RESULTS: Both [(15)O]O(2) and [(15)O]CO gasses could be produced in sufficient amounts, whilst meeting European Pharmacopeia requirements. Although produced oxygen-15 gasses contained a minor level of (11)C contamination, in clinical studies it was possible to correct for this contamination by delayed blood counting. CONCLUSION: An 11 MeV proton cyclotron combined with an in-house developed gas delivery system allows for the production and administration of sufficient amounts of [(15)O]-gasses for routine clinical PET studies in an hospital setting.

Validation protocol for current good manufacturing practices production of [15O]water for hybrid PET/MR studies.

INTRODUCTION: Oxygen-15 (O; t½ = 122.4 s) has been used for nuclear imaging experiments since the beginning of the field. With the advent of simultaneous hybrid PET/MR technology, [O]water has seen a resurgence and remains the gold standard method for quantitative blood flow studies. The short half-life presents a nontrivial challenge to applying current good manufacturing practices production methods to maintain patient safety. METHODS: A two-vial production method was devised to ensure adequate mixing of [O]water vapour into buffered isotonic saline. For production validation, six batches of [O]water were prepared: sterility, quality control testing and four patient doses. The final dose also underwent quality tested. Routine quality control testing included the following: radiochemical identity and purity, radionuclidic identity and purity, appearance, pH, pyrogenicity, and filter integrity. Sterility was retrospectively confirmed. For validation, breakthrough Pt concentration was also measured. RESULTS: Consistent yields of 10-12 GBq (270-325 mCi) were obtained 3 min after bombardment. Overall, 26 [O]water batches underwent quality control testing under this protocol and all met or exceeded release specifications for clinical use. CONCLUSION: The multiple batch protocol proved to be a safe and effective means for producing [O]water. Furthermore, this protocol could be readily adapted by any facility attempting to produce [O]water for clinical studies. Compared with previous attempts at our site, the protocol outlined here was more consistent and reliable, improved production workflow and led to more available radioactivity for participant injection and QC testing.

Bio-inspired arene cis-dihydroxylation by a non-haem iron catalyst modeling the action of naphthalene dioxygenase.

Reported in this paper is the first example of a biomimetic iron complex, ([Fe(II)(TPA)(NCMe)(2)](2+) (TPA = tris(2-pyridylmethyl)amine), that catalyses the cis-dihydroxylation of an aromatic double bond, mimicking the action of the non-haem iron enzyme naphthalene dioxygenase and shedding light on its possible mechanism of action.

Influence of residual oxygen-15-labeled carbon monoxide radioactivity on cerebral blood flow and oxygen extraction fraction in a dual-tracer autoradiographic method.

OBJECTIVE: Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO(2)), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) are quantitatively measured with PET with (15)O gases. Kudomi et al. developed a dual tracer autoradiographic (DARG) protocol that enables the duration of a PET study to be shortened by sequentially administrating (15)O(2) and C(15)O(2) gases. In this protocol, before the sequential PET scan with (15)O(2) and C(15)O(2) gases ((15)O(2)-C(15)O(2) PET scan), a PET scan with C(15)O should be preceded to obtain CBV image. C(15)O has a high affinity for red blood cells and a very slow washout rate, and residual radioactivity from C(15)O might exist during a (15)O(2)-C(15)O(2) PET scan. As the current DARG method assumes no residual C(15)O radioactivity before scanning, we performed computer simulations to evaluate the influence of the residual C(15)O radioactivity on the accuracy of measured CBF and OEF values with DARG method and also proposed a subtraction technique to minimize the error due to the residual C(15)O radioactivity. METHODS: In the simulation, normal and ischemic conditions were considered. The (15)O(2) and C(15)O(2) PET count curves with the residual C(15)O PET counts were generated by the arterial input function with the residual C(15)O radioactivity. The amounts of residual C(15)O radioactivity were varied by changing the interval between the C(15)O PET scan and (15)O(2)-C(15)O(2) PET scan, and the absolute inhaled radioactivity of the C(15)O gas. Using the simulated input functions and the PET counts, the CBF and OEF were computed by the DARG method. Furthermore, we evaluated a subtraction method that subtracts the influence of the C(15)O gas in the input function and PET counts. RESULTS: Our simulations revealed that the CBF and OEF values were underestimated by the residual C(15)O radioactivity. The magnitude of this underestimation depended on the amount of C(15)O radioactivity and the physiological conditions. This underestimation was corrected by the subtraction method. CONCLUSIONS: This study showed the influence of C(15)O radioactivity in DARG protocol, and the magnitude of the influence was affected by several factors, such as the radioactivity of C(15)O, and the physiological condition.

Clinical impact of hemodynamic parameter measurement for cerebrovascular disease using positron emission tomography and (15)O-labeled tracers.

Positron emission tomography (PET) measurement of cerebral blood flow and metabolism has been a basic and standard method for evaluation of hemodynamics in patients with cerebral vascular disease (CVD). Despite the recent rapid spread of PET and PET/CT facilities, the number of patient examinations with (15)O-gas PET scans is declining because most facilities are used for cancer studies. They avoid (15)O-gas PET study because it is time consuming and the technique and calculation methods appear to be complicated. However, reconsidering the benefits and usefulness of conventional (15)O-gas PET study is a good opportunity to understand its potential possibility. Physiological evaluation of cerebral perfusion and metabolism provided the basic concept of hemodynamics in impaired circulation and the development of evidence-based medicine in neurosurgical treatment for CVD. This method can be used for two major objectives, clinical examination with a less-invasive simplified method, and quantitative precise measurements with model analysis for research purposes. Both are important for developing further practical and investigational approaches using (15)O-gas PET.

Production of 15O for Medical Applications via the 16O(γ,n)15O Reaction.

15O (half-life, 122 s) is a useful radionuclide for PET applications. Current production of 15O typically makes use of the 14N(d,n)15O, 15N(p,n)15O, or 16O(p,pn)15O reactions using an accelerator. A novel approach for the production of 15O is via the 16O(γ,n)15O reaction using an electron linear accelerator. Photonuclear reactions using an electron linear accelerator may allow for feasible and economical production of 15O compared with the current methods. Methods: In this work, experiments using a repurposed Clinac were conducted using oxygen-containing alumina as a target material to study the production rate of 15O. Additional studies were conducted using a water target cell. Simulations using Geant4 were conducted to predict the activity and power dissipation in the target. Results: Bremsstrahlung radiation from the electron beam, and consequently 15O production via photonuclear reactions, is enhanced when a high-Z material, tungsten, is placed in front of the target. The alumina irradiations provided preliminary data to optimize the beam parameters and target configuration. The optimal thickness of tungsten was 1.4 mm for both the simulated and the measured studies of alumina. Simulations of irradiated water targets showed that tungsten thicker than 1.4 mm resulted in fewer photons available to activate the water; thus, a higher current was required to achieve a fixed dose. Alternatively, for a constant tungsten thickness, more power was deposited in the target with increasing beam energy, requiring a lower current to achieve a fixed dose. Actual irradiations of a water target yielded a quantity of 15O in the water that was consistent with expectations based on irradiations of alumina. Conclusion: Several parameters should be considered regarding the photonuclear production of 15O for an average patient dose of 1,850 MBq (50 mCi) in 10 mL. This work illustrates a variety of machine parameters capable of achieving a reasonable patient dose. Our simulations show that the power deposited in the target for these parameters is less than that in commercially operated cyclotron targets for the production of 18F. Thus, this work demonstrates that the photonuclear production of 15O may be a new production path for this useful radionuclide.

Assessment of Coronary Flow Velocity Reserve in the Left Main Trunk Using Phase-contrast MR Imaging at 3T: Comparison with 15O-labeled Water Positron Emission Tomography.

PURPOSE: The aim of this study was to verify coronary flow velocity reserve (CFVR) on the left main trunk (LMT) in comparison with myocardial flow reserve (MFR) by 15O-labeled water positron emission tomography (PET) (MFR-PET) in both the healthy adults and the patients with coronary artery disease (CAD), and to evaluate the feasibility of CFVR to detect CAD. METHODS: Eighteen healthy adults and 13 patients with CAD were evaluated. CFVR in LMT was estimated by 3T magnetic resonance imaging (MRI) with phase contrast technique. MFR-PET in the LMT territory including anterior descending artery and circumflex artery was calculated as the ratio of myocardial blood flow (MBF)-PET at stress to MBF-PET at rest. RESULTS: There was a significant positive relationship between CFVR and MFR-PET (R = 0.45, P < 0.0001). Inter-observer calculations of CFVR showed good correlation (R2 = 0.93, P < 0.0001). The CFVR in patients with CAD was significantly lower than that in healthy adults (1.90 ± 0.61 vs. 2.77 ± 1.03, respectively, P = 0.01), which were similar to the results of MFR-PET (2.23 ± 0.84 vs. 3.96 ± 1.04, respectively, P < 0.0001). For the detection of patients with CAD, the area under the curve was 0.78 (P = 0.01). The sensitivity was 0.77 and specificity was 0.72 when a cut-off of 2.15 was used. CONCLUSION: CFVR by 3T was validated with MFR-PET. CFVR could detect the patients with CAD. This method is a simple and reliable index without radiation or contrast material.

Synthesis of 11C, 18F, 15O, and 13N radiolabels for positron emission tomography.

Positron emission tomography (PET) is a powerful and rapidly developing area of molecular imaging that is used to study and visualize human physiology by the detection of positron-emitting radiopharmaceuticals. Information about metabolism, receptor/enzyme function, and biochemical mechanisms in living tissue can be obtained directly from PET experiments. Unlike magnetic resonance imaging (MRI) or computerized tomography (CT), which mainly provide detailed anatomical images, PET can measure chemical changes that occur before macroscopic anatomical signs of a disease are observed. PET is emerging as a revolutionary method for measuring body function and tailoring disease treatment in living subjects. The development of synthetic strategies for the synthesis of new positron-emitting molecules is, however, not trivial. This Review highlights key aspects of the synthesis of PET radiotracers with the short-lived positron-emitting radionuclides (11)C, (18)F, (15)O, and (13)N, with emphasis on the most recent strategies.

Calculation of the positron distribution from 15O nuclei formed in nuclear reactions in human tissue during proton therapy.

To measure and verify the dose distribution within a patient during proton therapy, indirect methods must be used. One such method is to use positron emission tomography (PET), which takes advantage of the nuclear reactions that take place between protons and nuclei in the tissue. The dominant nuclear reaction in human muscle tissue involves oxygen nuclei and produces radioactive oxygen-15. Oxygen-15 decays through positron emission, and it is these positrons that go on to annihilate that produce the signal used in the PET technique. Finding the distribution of annihilation points, however, is not analogous to finding the proton dose distribution. The oxygen-15 and positrons travel finite distances within the tissue, blurring the detected PET distribution from the desired proton distribution. Through Monte Carlo modelling, an analysis of the differences between the positron, oxygen-15 and proton distributions has been made. The program SRIM 2003 was used to find the correlation between the three distributions within simulated muscle tissue. Results show that the distal edge of the proton Bragg peak correlates with the detectable positron distribution, which is a section of the dose distribution of interest due to the steep dose gradient and position of adjacent critical structures.

Binding of 11C-Pittsburgh compound-B correlated with white matter injury in hypertensive small vessel disease.

OBJECTIVE: 11C-Pittsburgh compound-B (11C-PIB) positron emission tomography (PET) is used to visualize and quantify amyloid deposition in the brain cortex in pathological conditions such as Alzheimer's disease (AD). Intense 11C-PIB retention is also observed in the white matter (WM) of both healthy individuals and AD patients. However, the clinical implications of this retention in brain WM have not been clarified. We investigated the relationship between the extent of white matter lesions (WMLs) and the binding potential of 11C-PIB (BPND) in the WM in patients with hypertensive small vessel disease. We further examined the relationship between the extent of WMLs and BPND in WML and in normal-appearing white matter (NAWM). METHODS: Twenty-one hypertensive vasculopathy patients, without AD and major cerebral arterial stenosis and/or occlusion, were enrolled (9 women, 68 ± 7 years). Regions of WML and NAWM were extracted using magnetization-prepared rapid gradient-echo and fluid-attenuated inversion recovery of magnetic resonance images. Volumes of interest (VOIs) were set in the cortex-subcortex, basal ganglia, and centrum semiovale (CS). BPND in the cortex-subcortex, basal ganglia, CS, WML, and NAWM were estimated on 11C-PIB PET using Logan graphical analysis with cerebellar regions as references. The relationships between WML volume and BPND in each region were examined by linear regression analysis. RESULTS: BPND was higher in the CS and basal ganglia than in the cortex-subcortex regions. WML volume had a significant inverse correlation with BPND in the CS (Slope = -0.0042, R 2 = 0.44, P < 0.01). For intra WM comparison, BPND in NAWM was significantly higher than that in WML. In addition, although there were no correlations between WML volume and BPND in WML, WML volume was significantly correlated inversely with BPND in NAWM (Slope = -0.0017, R 2 = 0.26, P = 0.02). CONCLUSIONS: 11C-PIB could be a marker of not only cortical amyloid-ß deposition but also WM injury accompanying the development of WMLs in hypertensive small vessel disease.

Production of [15O]water at low-energy proton cyclotrons.

We report a simple system for producing [15O]H2O from 15N in a nitrogen/hydrogen gas target with recycling of the target nitrogen, allowing production on low-energy proton-only accelerators with minimal consumption of isotopically enriched 15N. The radiolabeled water is separated from the target gas and radiolytically produced ammonia by temporary freezing in a small trap at -40 degrees C.

Corrections for the combined effects of decay and dead time in live-timed counting of short-lived radionuclides.

Studies and calibrations of short-lived radionuclides, for example (15)O, are of particular interest in nuclear medicine. Yet counting experiments on such species are vulnerable to an error due to the combined effect of decay and dead time. Separate decay corrections and dead-time corrections do not account for this issue. Usually counting data are decay-corrected to the start time of the count period, or else instead of correcting the count rate, the mid-time of the measurement is used as the reference time. Correction factors are derived for both those methods, considering both extending and non-extending dead time. Series approximations are derived here and the accuracy of those approximations are discussed.

Delayed contrast enhancement and perfusable tissue index in hypertrophic cardiomyopathy: comparison between cardiac MRI and PET.

UNLABELLED: Delayed contrast enhancement (DCE) visualized by cardiac MRI (CMR) is a common feature in patients with hypertrophic cardiomyopathy (HCM), presumed to be related to myocardial fibrosis. The pathophysiologic basis of hyperenhancement in this patient group, however, remains unclear as limited histologic comparisons are available. The present study compares the perfusable tissue index (PTI), an alternative marker of myocardial fibrosis obtained by PET, with DCE-CMR in HCM. METHODS: Twenty-one patients with asymmetric septal HCM, 12 chronic myocardial infarction (MI) patients, and 6 age-matched healthy control subjects were studied with DCE-CMR and PET. PET was performed using (15)O-labeled water and carbon monoxide to obtain the PTI. RESULTS: No hyperenhancement was observed in control subjects and the PTI was within normal limits (1.10 +/- 0.07 [mean +/- SD]). In MI patients, the extent of hyperenhancement (25% +/- 16% [mean +/- SD]) was inversely related to the decrease in the PTI (0.94 +/- 0.12; r = -0.65, P < 0.05). Average hyperenhancement in HCM was 14% +/- 12%, predominantly located in the interventricular septum. The PTI in the hypertrophied interventricular septum, however, was not reduced (1.12 +/- 0.13). Furthermore, in contrast to MI patients, there was a modest positive correlation between the extent of DCE and the PTI in HCM (r = 0.45, P < 0.05). CONCLUSION: DCE in the hypertrophied septum of HCM patients is not accompanied by a decline in the PTI, and there is a positive correlation between the extent of DCE and the PTI. These results suggest that hyperenhancement may not be caused solely by fibrotic replacement scarring in this patient group. Other pathologic changes associated with HCM may also cause gadolinium-diethylenetriaminepentaacetic acid hyperenhancement.

Identification of oxygen-19 during in vivo neutron activation analysis of water phantoms.

Hand bone equivalent phantoms (250 ml) carrying selenium in various amounts were irradiated and counted for in vivo neutron activation analysis (IVNAA) by employing a 4π NaI(TI) based detection system. During the analysis of counting data, a feature at a higher energy than the gamma ray peak from (77m)Se (0.162 MeV) was observed at 0.197 MeV. Further investigations were made by preparing water phantoms containing only de-ionized water in 250 ml and 1034 ml quantities. Neutrons were produced by the (7)Li(p,n)(7)Be reaction using the high beam current Tandetron accelerator. Phantoms were irradiated at a fixed proton energy of 2.3 MeV and proton currents of 400 µA and 550 µA for 30 s and 22 s respectively. The counting data saved using the 4π NaI(TI) detection system for 10 s intervals in anticoincidence, coincidence and singles modes of detection were analyzed. Areas under gamma peaks at energies 0.197 MeV and 1.357 MeV were computed and half-lives from the number of counts for the two peaks were established. It was concluded that during neutron activation of water phantoms, oxygen-18 is activated, producing short-lived radioactive 19O having T(1/2) = 26.9 s. Induced activity from 19O may contribute spectral interference in the gamma ray spectrum. This effect may need to be taken into account by researchers while carrying out IVNAA of biological subjects.